Hum reduction



Nov. 26, 1940. R, B. DOME 2,223,206

HUM REDUCTION Filed 001;. 26, 1-938 Invent or- Rob ert' BkDome,

H is Attorney-- Patented Nov. 26, 1940 UNITED? STATES PATENT O -WHY REDUCTION Robert B. Dome, Bridgeport,. Conn, assignor to General Electric Company, a corporation of New York Application October 26, 193&, Serial No. 237,024

6 Claims.

My invention relates to; electrondischarge, cir cuits and more particularly to means for reducing so-called hum currents in such-circuits;

Electron discharge devices in which the-cathodes are heated by alternating current applied- Such hum currents are produced by reason of a number of different efiects. It has been found.

in accordance with my invention that they may be produced by reason of capacity existing between the lead-in conductors of the grid and heater of the discharge device; It has also been found in accordance with my invention, that the heater may act as a grid within. the. discharge device to vary the current flowing from the anode to the cathode.

One of the objects of my invention is to, reduce the hum currents produced by either of these efiects.

Another object of my invention is to supply to the grid of the electron discharge device an electromotive force tending to neutralize the effect of the heater element acting as a gird within the discharge device.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanyingdrawing in which Fig. 1 represents an embodiment of my invention; Fig. 2 represents a structural detail of an electron discharge device inconnection with which my invention may be employed; and Fig. 3 represents a modification of my invention.

Referring first to Fig. 2 of the drawing, I have indicated therein the arrangement of the lead-in conductors of an electron discharge device in connection with which my invention may be employed. This figure represents the base of an electron discharge device having projecting therefrom a number of terminals l to 8 inclusive, certain of these terminals, of course, being connected to electrodes within the discharge device through lead-in conductors. I have also indicated on this drawing by suitable legends the electrode to which the respective terminals are connected. The shell or metal envelope of the discharge device, which is connected to the terminal 4, is-commonly'connected through externalconnections to the heater terminal 3'and to ground becauseof thegreater convenience of wiring adjacent terminals together. The opposite heater terminal 1, it willbeobserved, is adjacent thecontrol gridterminal- 6. I have found that the, capacity between these twoterminals, or more particularly between'the lead-in conductors extendingv from these terminals up through the glass seal, which capacity I have indicated by dotted lines- 9 in the figure, is sure ficient to induce into the grid circuit of thedischarge device an objectional amount of voltage from the heater circuit. In fact, this voltage after amplification in two-or three amplification stages may amount to as much. as 10 volts andis thus decidedly objectionable. I have found that this voltage, may be, very substantially reduced-by grounding the heater terminal I through the external connections, this, terminal. being the one. nearer to the control grid. The, shell terminal! is then connected to terminal 1 and terminalt is of course not grounded. I

In fact, this change in circuit connection has been found to reduce the hum voltage produced by the capacity 9 to as low as one quarterof its initial value. 1 In Fig. 1 I have shown the circuit embodying my invention in more complete detail. In this figure I have shown an electron discharge device l0 having a cathode which is connected through a cathode bias resistor ll to ground and to the terminal I of the heater. It is'also connected through terminal 4 to the envelope of the. electron discharge device. The source of heating current which is represented bythe cathode transformer I2 is connected directly across the heater, i. e., between terminals 3 and l. M

The figure also represents an input circuitof the discharge device comprising an input coupling condenser I3 and resistance Hi, the latter of which is connected between the control grid and cathode of the discharge device through the bias resistor H. An output circuit is shoWncompr'is ing the coupling condenser 15, anode coupling resistor l6, and source of anode potential l1. Screen grid potential for the discharge device is supplied by the source I8. The sources 11-, i8; and similarly the cathode bias resistor l I, arebypassed for currents to be; amplified by the dis charge device, by condensers 19, 20, and 2| respectively.

With the connections shown it willbe observed that due to the cathode heating current supplied l 1 cathode which tends to oppose these variations in by transformer I 2, the potential of the heater varies cyclically with respect to the potential of the cathode. I have found that this heater has the effect of a grid within the discharge device in that when its potential varies in the positive direction, the current in the anode circuit increases, whereas when it .varies in the negative direction, the anode current decreases.

In accordance with my invention a voltage is supplied between the control grid and the anode current. It has been found convenient to supply this voltage across the cathode bias resistor'l I, and, in the form of the invention shown in Fig. 1, this is effected byitheshunticombination .of resistance 22 and capacitance 23, the latter being connected between the cathode of the discharge device and the terminal 3 or theheater. It has been found that by properly proportioning this resistanceand condenser relative to the resistance l I and condenser 2|, a voltage 'may'be produced across resistance ll tending tomake the grid sufficiently negative with respect to the cathode during the half cycles of the heating current when the anodecurrent tends to increase to 'just overcome these Variations. To effect this,it is merely necessary that the voltage supplied to the cathode through resistance 22 be in phase withthe voltage supplied to the heater, and it may easily be shown that this condition obtains whenthe time constant of resistance 22 and condenser 23 is equal to the time constant of resistor ll and condenser 2|. I have found that by the use of ,thisconnection, including resistanceZZ and condenser 23, the hum voltage may be reduced to substantially less thanhalf that which is produced when these elements are omitted from thecircuit. j

O'fjcourse the tendency of the anode current to increase due to variation ingthe heating'current isopposed toa slight'extent by the potential produced on resistance-ll by'the passage of this anode current. That is, an increaseflin anode.

current produces a larger potential on resistance II which, in turn,'drives the grid more'negative.

.foreffective elimination or hum it is-necessary to supply. a greater voltage across resistance H as is done by resistance 22 and condenser v23.

In Fig. 3 I have shown a modification of my invention in which the heatingcurrent is supplied from a transformer I 2 as. in Fig. 1. The secondary winding. of this transformer, however, has an intermediate point which is connected to the terminal I of the heater, the terminal at one end of the secondary winding being connected to the opposite terminal 3 of the heater, and the other terminal of the secondary winding being connected through gridcoupling resistor I 4 to the control grid of the discharge device. In thisto the cathode thereby tending to oppose the increase in anode current.

While I haveshown 'a particular embodiment of my invention, it will of course be understood that I do notwish to be limited thereto, since many modifications both in the circuit arrangementand instrumentalities employed may be made, and I contemplateby the appended claims to cover any such modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electron discharge device having a grid element, an anode element, a unipotential cathode element, and a heater element arranged to heatgsaid cathode all enclosed in a sealed envelope, lead-in conductors for said elements including a pair of lead-in conductors for said heater element, one of said pair of lead-in conductors for the heater element being physically nearer the lead-in conductor for the grid than the other,,an input circuit connected to said gridand cathode lead-in conductors, an output circuit connected to said anode and cathode leadin conductors, means to ground a point common to said circuits, a source of alternating electromotive force connected to said pair of lead-in conductors to energize said heater elements,

vice having a grid'circuit, an anode circuit, a

unipotential cathode, and a heater for said cathode, an impedance common tosaid circuits, said impedance being connected between said heater and cathode, means to supply alternating heating current to said heater whereby the potential'of said heater varies relative to said cathode, and tends to produce corresponding variations in current in said anode circuit, and means to supply across said impedance a voltage having the frequency of the heating current and phased to oppose said variations in anode current.

3. In combination, an electron discharge device having agrid circuit, an anode circuit, a unipotential cathode, and a heater for said cathode, an impedance common to said circuits, said impedance being connected between said cathode and one side of said heater, means to supply alternating heating current-to said heater, and an impedance between the cathode and the opposite side of'said heater, said impedances being proportioned to produce on said cathode a voltage of the frequency of the heating currents and phased to oppose variations in anode current produced by variation in potential of the heater relative to the cathode.

4. In combination, an electron discharge device having an anode, a unipotential cathode, a grid, and a heater for said cathode, a circuit between said anode and cathode, a source of a1- ternating energizing current connected across said heater and having one side thereof connected to said cathode whereby the potential of the heater varies with respect to the cathode, and said heater acts as a grid to control the current in said circuit, and means to supply between said grid and cathode from said source, a potential of phase with respect to the cathode potential opposite to that of said heater and of such value that acting on said grid it opposes the effect of the potential on the heater acting as a grid.

5. In combination, an electron discharge device having a grid circuit, an anode circuit, a unipotential cathode, and a heater for said cathode. a resistance common to said circuits, said resistance being connected between said heater and cathode and shunted by capacitance to supply bias voltage from the anode circuit to the grid circuit, a source of alternating current connected across said heater, one side thereof being connected through said resistance to said cathode whereby the potential of said heater varies with respect to said cathode and said heater acts as a grid to control the current in said anode circuit, a resistance connected between the opposite side of said source and said cathode, said resistance being shunted by a capacitance, said last resistance and capacitance having a time constant equal to the time constant of said first resistance and capacitance, whereby a potential is supplied to said grid circuit of proper phase to oppose said effect on the anode circuit of said heater acting as a grid.

6. In combination, an electron discharge device having an anode circuit, a grid circuit, a unipotential cathode and a heater for said cathode, a source of alternating'current having an intermediate point thereof connected to one side of said heater, to said cathode, and through said anode circuit to said anode, and points opposite said intermediate point connected to said grid end to the opposite side of said heater respectively, whereby said grid is supplied with a potential with respect to said cathode of opposite phase to that with respect to said cathode which is supplied to said heater and the magnitude of the potential supplied to said grid being just sufi'icient to neutralize the eifect on current in the anode circuit of the potential on the heater with respect to the cathode acting on said heater as a grid.

CERTIFICATE OF CORRECTION, Patent No, 2,225,206. November 26, 19%.

ROBERT B, DOME. 7 It is hereby certified that error appears in the printed specification of theabove numbered patent requiring correction as follows: Page 1, first column, line 29, for "gird" read "grid-"1 page}, second column, line ll claim 5, for the word "end" read and; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of, the case in the Patent Officeu Signed and sealed this lhthday of" January, A, 1). 19m

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents., 

